1. Field of the Invention
The present invention relates to a fuel cell system and, more particularly, to a technology for changing the passages in the fuel cell system in accordance with the type of cartridge loaded.
2. Description of the Related Art
A fuel cell is a device that generates electricity from hydrogen and oxygen so as to obtain highly efficient power generation. A principal feature of a fuel cell is its capacity for direct power generation which does not undergo a stage of thermal energy or kinetic energy as in conventional power generation. This presents such advantages as high power generation efficiency despite the small scale setup, reduced emission of nitrogen compounds and the like, and environmental friendliness on account of minimal noise or vibration.
Of various types of fuel cells, a polymer electrolyte fuel cell excels in its low operating temperature and high output density. Recently, direct methanol fuel cells (DMFC) are especially attracting the attention as a type of polymer electrolyte fuel cell. In a DMFC, methanol water solution as a fuel is not reformed and is directly supplied to the anode so that electricity is produced by an electrochemical reaction induced between the methanol water solution and oxygen. Discharged as reaction products resulting from the electrochemical reaction are carbon dioxide emitted from the anode and generated water emitted from the cathode. Methanol water solution has a higher energy density per unit volume than hydrogen. Moreover, it is suitable for storage and poses little danger of explosion. Accordingly, it is expected that methanol water solution will be used in power supplies for automobiles, mobile devices (cell phones, notebook personal computers, PDAs, MP3 players, digital cameras, electronic dictionaries and books) and the like.
Generally, methanol water solution used in a DMFC is supplied in the form of a detachable cartridge. A cartridge stores methanol water solution at higher concentration than the concentration optimal for power generation. The high concentration methanol is diluted in a diluted fuel tank in the fuel cell system before being supplied to a DMFC. This arrangement increases power generated per cartridge and improves the convenience of a DMFC (see, for example, patent document No. 1).
[patent document No. 1] JP 2004-152741
When a DMFC has just been purchased or when a DMFC is not scheduled to be used for a long period of time so that the diluted fuel tank is emptied for the purpose of storage, purified water needs to be supplied to the diluted fuel tank before using the DMFC. In this background, there are demands for a fuel cell system in which user maintenance such as supplying of purified water can be easily performed. Meanwhile, if user convenience is pursued too much and the structure of the fuel cell system becomes complicated as a result, it would be difficult to save space and cost.